Evidence for Extreme Cortical Flexibility: Higher Cognitive Functions in "Visual" Cortices of Blind Individuals
Embargo until
2019-12-01
Date
2018-10-24
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Johns Hopkins University
Abstract
Are structure and function inextricably linked in the brain? In the early 19th century, phrenologists endeavored to localize cognition to areas of the brain. Though neuroscientists have updated the methodology and the notion of what constitutes a mental process, the goal remains the same: to map functions to locations. But how flexible are these structure-to- function mappings? Studying adaptations of the “visual” cortex to blindness offers insight on the extent to which brain structures can carry out functions for which they did not evolve.
In this dissertation, I ask how flexible visual cortices are in the absence of expected visual information. I examine the ability of blind individuals’ occipital cortices to take on functions that are higher cognitive and, therefore, radically different from vision. First, Chapter 2 explores the extent of higher cognitive takeover of “visual” cortices in blindness. Using naturalistic stimuli, I find that “visual” cortices of blind individuals synchronize to a shared interpretive, rather than a shared perceptual, experience. This suggests systematic and widespread repurposing of “visual” cortices for higher-cognitive functions. Next, Chapter 3 asks whether “visual” cortices of blind individuals are repurposed for higher cognitive functions other than language, and executive functions in particular. I find evidence for executive functions in primarily right-lateralized “visual” cortices using both a non-verbal response-inhibition task and by examining functional connectivity at rest. Finally, Chapter 4 examines the functional relevance of previously observed language and executive function responses in the “visual” cortices of blind individuals. I find that blind individuals are better than matched sighted controls at comprehending syntactically complex sentences and at inhibiting prepotent button pressing. This suggests that repurposed “visual” cortices may confer a behavioral advantage.
Taken together, this dissertation demonstrates that “visual” cortices of blind individuals are meaningfully repurposed for higher cognitive functions. Though brain structures may seem particularly suited to implement a particular function, such structure- to-function mappings are not evidence of functional rigidity. In contrast, evidence from blindness suggests that human cortex is highly flexible at birth.
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Keywords
Plasticity, Vision, Neuroplasticity, Visual Cortex, Blindness